Studies on spacer molecules and coupling agents for immobilising glucose oxidase on nylon mesh for glucose oxidase electrodes

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Abstract
An alternative coupling agent to glutaraldehyde, namely, p-benzoquinone, has been used together with various spacer molecules for the immobilisation of glucose oxidase on nylon mesh. The spacer molecules studied were the amino acids asparagine, arginine, lysine, glutamine and ornithine and the aromatic diamines, p-phenylenediamine and m-phenylenediamine. Nylon net activated with dimethyl sulphate, and activated nylon net reacted with either p-benzoquinone or glutaraldehyde but with no spacer, were used as controls. The various enzyme electrodes were screened by monitoring glucose amperometrically using a platinum working electrode covered with the nylon net immobilised with glucose oxidase at 600 mV versus a silver-silver chloride reference and a glassy carbon auxiliary electrode system. It was found that the current output of the enzyme electrodes for immobilisation with each of the coupling agents decreased in the order lysine > arginine > asparagine > p-phenylenediamine > ornithine > m-phenylenediamine > glutamine > no spacer system > activated nylon membranes, indicating that the most active enzyme membranes are obtained with the lysine spacer. However, the p-benzoquinone coupled systems gave higher currents and the enzyme electrodes showed an increased glucose detection range, 0.001–5 mM glucose compared with 0.001–2 mM glucose for the glutaraldehyde systems. The electrodes showed robust behaviour with respect to prolonged exposure to glucose, while the lifetimes of all the membrane electrodes were ca. 4 months when stored at 4 °C in pH 7 buffer with intermittent use.

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